This application is based on Patent Application No. 2000-142455 filed in Japan, the content of which is hereby incorporated by reference.
(1) Field of the Invention
The present invention relates to a glass bulb for a cathode-ray tube (hereafter called xe2x80x9cCRTxe2x80x9d), and a CRT device equipped with a CRT glass bulb.
(2) Description of Related Art
In general, a CRT device is roughly made up of a CRT glass bulb and a number of members attached to outside of the glass bulb. The CRT glass bulb is made by integrating a plurality of glass members which include a phosphor screen, an internal electrode film, or the like and sealing with an electron gun that emits an electron beam in high vacuum. The number of members includes a deflection yoke to deflect the electron beam. The construction of the conventional CRT glass bulb is briefly described below.
FIG. 1 is a schematic sectional view to show an example construction of the conventional CRT glass bulb. As shown in the figure, the conventional CRT glass bulb is made by integrating a glass member 901 that forms a panel unit, a glass member 902 that forms a funnel unit, and a glass member 903 that forms a neck unit, and sealing with a glass frit or heat fusing. On an inner surface of the glass bulb, an internal electrode film 906 is formed and connected to an anode button 907 in a conductive state. The anode button 907 are extended to the outside of the glass bulb through the funnel unit glass member 902.
When compared with other types of display devices that have developed in recent years such as a liquid crystal display panel and a plasma display panel, a CRT device has a large depth, which is a major drawback. Therefore, reducing the depth is one of the important issues in developing CRT devices. However, to reduce the depth of the CRT device equipped with the glass bulb described above, mainly a depth L2 of the funnel unit has to be reduced.
The conventional funnel unit glass member 902 is formed in one piece using pressing. Accordingly, reducing the depth of the funnel unit glass member 902 deteriorates vacuum strength and implosion-proof of the glass bulb. Therefore, the reduction of the depth of the funnel unit has already reached its limits due to the design constraints on the strength.
An object of the present invention is to provide a glass bulb for a CRT whose funnel unit have a less depth than a conventional one and a CRT device equipped with the CRT glass bulb.
First, the circumstances which led the inventors to the present invention is described. In forming the funnel unit in one piece as explained in the related art, the inventors designed a prototype of a funnel unit glass member 902 to reduce the depth of the funnel unit and at the same time to improve vacuum strength and implosion-proof. However, the prototype was broken in the pressing process and ended in failure.
The inventors examined the cause of the failure and made the following assumption. The funnel unit glass member 902 and a panel unit glass member 901 are joined at a sealed portion. Here, the sealed portion indicates a portion where two glass members are joined by sealing. Therefore, the thickness of the portion of the funnel unit glass member 902 which is to be joined to the panel unit glass member 901 needs to be substantially the same as the thickness of the portion of the panel unit glass member 901 which is to be joined to the funnel unit glass member 902. In consideration of (a) the strength of a seal used for sealing the sealed portion and (b) increase of stress to the sealed portion caused by reducing the depth of the funnel unit, the sealed portion between the panel unit glass member 901 and the funnel unit glass member 902 is preferably as thick as 15 mm to 30 mm.
On the other hand, in a sealed portion between the funnel unit glass member 902 and a neck unit glass member 903, thickness of the portion of the funnel unit glass member 902 which is to be joined to the neck unit glass member 903 also needs to be substantially the same as the thickness of the portion of the neck unit glass member 903 which is to be joined to the funnel unit glass member 902. However, members such as a deflection yoke for deflecting an electron beam have to be provided around the sealed portion. Hence, it is necessary to make the sealed portion thin in order to increase the magnetic flux density of the deflection yoke.
Consequently, the conventional funnel unit glass member 902 needs to be approximately 15-30 mm thick at the portion which is to be joined to the panel unit glass member 901 and approximately 2-3 mm thick at the portion which is to be joined to the neck unit glass member 903. When the funnel unit is formed from a single glass member, a maximum-to-minimum thickness ratio of the funnel unit glass member 902 is approximately 10:1.
The inventors assumed that the prototype of the funnel unit glass member was broken because such a large maximum-to-minimum thickness ratio of the funnel unit glass member 902 caused the difference in cooling rates during the pressing process between the thickest portion and the thinnest portion of the funnel unit glass member 902. In other words, if the maximum-to-minimum thickness ratio had been set within a certain range, it would have been possible to make the sealed portion between the funnel unit glass member 902 and the panel unit glass member 901 sufficiently thick.
Based on the above assumption, the inventors has invented a glass bulb for a cathode-ray tube including: a panel unit having a panel screen; a neck unit holding an electron gun; and a funnel unit having a funnel-like shape, wherein the panel unit and the neck unit are bridged by the funnel unit, wherein the funnel unit is formed from a plurality of glass members, the plurality of glass members including at least a first glass member on a side of the panel unit and a second glass member on a side of the neck unit, and wherein a maximum-to-minimum thickness ratio of each of the plurality of glass members is designed to be within a range suitable for producing the plurality of glass members using pressing, the maximum-to-minimum thickness ratio being a ratio of thickness of a thickest portion to thickness of a thinnest portion.
With this construction, the portion of the funnel unit glass member 902 which is to be joined to a panel unit glass member 901 can be made thicker enough to improve the vacuum strength and the implosion-proof while reducing the depth of the funnel unit. Here, the range of the maximum-to-minimum thickness ratio suitable for producing the glass members using pressing is likely to vary depending on which type of glass material is used. For example, when a glass material conforming to EIAJ (Electronic Industries Association of Japan)xc2x7LOF-03 is used, the inventors found that the maximum thickness needs to be no more than about five times the minimum thickness.
Also, the inventors examined to use strengthened glass for the funnel unit in order to further improve the vacuum strength and the implosion-proof. The physical strengthening can be performed by air-cooling the glass member molded by pressing, heating it again to a temperature which is 20-40xc2x0 C. lower than an annealing point, and cooling it slowly.
The inventors confirmed that if the maximum-to-minimum thickness ratio is in the suitable range for producing the glass member using pressing, it is possible to physically strengthen the glass member.
Therefore, by physically strengthening at least one glass member out of the plurality of glass members which form the funnel unit, strengthened glass can be used in at least part of the funnel unit. As a result, even if the depth of the funnel unit is reduced, the vacuum strength and the implosion-proof can be improved.
Here, the plurality of glass members that form the funnel unit is preferably joined by sealing with a glass frit so that the inside of the glass bulb is kept in a vacuum state. This is because, under the present circumstances, it is not preferable to use a method such as fusion sealing to seal strengthened glass.
Also, the funnel unit is formed from two glass members: a glass member to be joined to the panel unit grass member and a glass member to be joined to a neck unit glass member. The former funnel unit glass member and the latter funnel unit glass member are preferably joined at a position including an inflection point on a periphery of the funnel unit on a supposed plane substantially perpendicular to the tube axial direction. In consideration of a general shape of a glass bulb, the thickness of the glass bulb changes most sharply around the position. If the funnel unit is cut at the position, it can be efficiently divided into a thick glass member and a thin glass member. Also, the glass members with such shapes are easy to produce. Furthermore, each area of the sealed portion is sufficiently large. Therefore, this construction is preferable in consideration of the strength of the integrated glass bulb.
Also, when a shape of an original member to form the funnel unit glass member which is to be joined to the panel unit glass member is substantially the same as a shape of the panel unit glass member, it is possible to attempt to reduce a cost of a mold for molding the glass member. Here, xe2x80x9cthe shape of the original memberxe2x80x9d indicates the shape of the panel unit glass member when a shape of the funnel unit glass member is substantially the same as a shape in which a certain portion is removed from the panel unit glass member.
Among the plurality of glass members that form the funnel unit, the glass member which is to be joined to the panel unit glass member is preferable to be formed in one piece and physically strengthened. With this construction, strengthened glass is used around a sealed portion between the panel unit and the funnel unit. As a result, the sealed portion can be thinner, and the glass bulb can be lightened.
The glass bulb has a lead terminal connected to each internal electrode film which is provided on an inner surface of the funnel unit. The lead terminal is preferably extended to the outside of the glass bulb through a sealed portion between two out of the plurality of funnel unit glass members. In the conventional method, the lead terminal is provided so as to pass through the funnel unit glass member by heating part of it. However, for example, when all the funnel unit glass members are physically strengthened, the conventional method cannot be used because it is not preferable to heat strengthened glass to pass the lead terminal through the funnel unit glass members under the present circumstances.
Also, it is preferable to physically strengthen the panel unit glass member, so that the whole glass bulb is strengthened.
Moreover, the object is achieved by a glass bulb for a CRT including: a panel unit having a panel screen; a neck unit holding an electron gun; and a funnel unit having a funnel-like shape, wherein the panel unit and the neck unit are bridged by the funnel unit, and wherein physically strengthened glass is used in at least part of the funnel unit.
The object is further achieved by a manufacturing method of a glass bulb for a CRT including: a panel unit having a panel screen; a neck unit holding an electron gun; and a funnel unit having a funnel-like shape, wherein the panel unit and the neck unit are bridged by the funnel unit, the manufacturing method including: a glass member preparing step for preparing at least one physically strengthened glass member for the funnel unit, the funnel unit being formed from a plurality of glass members; and a glass bulb forming step for forming the glass bulb from the plurality of glass members including the glass member which is prepared in the glass member preparing step. Here, in the glass member preparing step, the glass members may be prepared by buying as well as by producing.
Additionally, the object is achieved by a CRT device equipped with the glass bulb of the present invention or the glass bulb produced according to the manufacturing method of the present invention.